390 MANUAL OF THE MOLLUSC A. 



but is a member of of a group characteristic of tropical America (to which the 

 names Plecochihis, Pachi/otis and Caprella have been given) including B. 

 signatus, B. bilabiatus, B. goniostomus, and especially B. sulcafus (Chilo- 

 nopsis, Fischer) of St. lago.* The four nest species belong to the same type, 

 but are smaller and slenderer. " The marine mollusks of the coast of St. 

 Helena would lead us to infer the very ancient isolation of that island, whilst 

 at the same time a pre-existing closer geographical relationship between the 

 African and the American continents than now maintains is dimly indicated. 

 The information we have obtained respecting the extinct and existing terres- 

 trial mollusks would seem to point in the same direction, and assuredly to 

 indicate a closer geographical alliance between St. Helena and the east coast 

 of S. America than now holds." — (Forbes), 



Tristan df Aciinlm. (No. 29 of Map). 



Two peculiar species of Balea (Tristensis and ventricosus) are found on this 

 remote and lofty island, which attains an elevation of 8,236 feet. 



3. African Region. 



Tropical Western Africa, with its hot and swampy coasts and river valleys 

 is the region of the great Achatina and Achatina4ike Bttlimi, the largest of 

 all living land-snails. Dr. Pfeiffer enumerates — Vitrina 8 sp. Strepaxis 7, 

 Helix 8, Piifa 5, BiiUmus 85, Achatitia 39, Succinea, 3. Streptaxis Reclu- 

 ::/ana inhabits the Guinea Islands. Helix Folini, Bnlimus numidicus and 

 fastigiattis, Pupa crt/stallum. and sorghum, Achatina columna, striatella and 

 loiophaga are found ou Princes Island. Phjm piifilla on Goree Island- 

 Bixlimus {Pseudachatina) Djwnesi, Acliatina iostoma and Glandina cerea 

 at Fernando Po. The reversed river-snail {Lanistes) is generally diffused in 

 the fresh waters of Africa ; several species of Potamides and Vihex are found 

 in the embouchures of the western rivers and Pedipes on the sea-shore. The 

 freshwater bivalves of Senegal are similar to those of the Nile ; — 

 Pisidium parasitirum, Egypt. Iridiiia exotica, Senegal. 



Cyrenoides Dnponti, Senegal. „ rubenS: „ 



Corbicula, 4 sp. -Egypt. Pleiodon ovatus „ 



Jridina nilotica „ J^theria semilunata „ Nile. 



,, aegyptiaca „ Galatea radiata „ 



4. Cape Region. 

 Dr. Kvauss describes 41 species of land-snail from South Africa, and Mr. 

 Benson has furnished a list containing 22 others ; these are all peculiar, 

 except a Succinea which appears to be only a variety of the European 



* As Dr. Pfeiffer includes this (with a sign of doubt) amongst the synonymes of 

 B. auris-vulpinus he must have suspected that the specimens came from St. Helena 

 and not from St. lago. The only other group of Bulimi resembling the St Helena 

 shells occurs in the Pacific Islands ■.—Bulimus Caledonicus at Mulgrave l.—B. auris 

 zoviiidi at the Solomons, and B. ahongi in New Zealand. 



